<template>
  <div class="box">
    <h2>child</h2>
    {{ username }}
  </div>
</template>

<script>
export default {
  data() {
    return {
      username: "zs",
    };
  },
  methods: {
    fn() {
      this.username = "李四";
    },
  },
};
</script>

<style>
</style>